Spatially distributed modelling of soil erosion and sediment yield at regional scales in Spain

Initiated by the need to quantify erosion rates and the impacts of global changes on erosion, several attempts have been made to apply erosion models at regional scales. However, these models have often been directed towards on-site soil erosion estimates, emphasising sheet and rill erosion processes, and disregarding gully erosion, channel erosion and sediment transport. These models are therefore of limited use for the assessment of sediment yield, off-site impacts of erosion, and for the development of environmental management to control these impacts at regional scale. This study analyses and compares three spatially distributed models for the prediction of soil erosion and/or sediment yield at regional scales: the WATEM-SEDEM model that is based on the empirical Revised Universal Soil Loss Equation (RUSLE) in combination with a sediment transport equation, the physics-based Pan European Soil Erosion Risk Assessment model (PESERA), and a newly developed Spatially Distributed Scoring model (SPADS). The three models were applied to 61 Spanish drainage basins and model predictions were evaluated against data on measured reservoir sedimentation rates. Global data sets on land use, climate, elevation and soil characteristics were used as model input for WATEM-SEDEM and SPADS, whereas published soil erosion estimates of PESERA at 1 km² resolution were used directly. SPADS and WATEM-SEDEM provided best results after separate calibration for basins with a Sediment Delivery Ratio (SDR) higher than 5% and those with an SDR lower than 5%. In this way, SPADS explained 67% of variation in sediment yield, while WATEM-SEDEM explained 48% of the variation. PESERA represents a promising alternative to the use of empirical models at the regional scale as it can be applied to very diverse environments with little calibration. However, PESERA provides soil erosion rates and not sediment yield estimates. For most basins PESERA soil erosion rates vary between fifty and close to zero percent of total sediment yield. Two major factors may explain this discrepancy between modelled soil erosion rates and measured sediment yield. First, it may be that PESERA underestimates soil erosion under Mediterranean conditions, although PESERA soil erosion rates are of the same order of magnitude as erosion rates measured in erosion plot studies. Second, gully-, river channel erosion and sediment transport processes may be much more important than sheet- and rill erosion for regional scale sediment yield in these environments. These issues therefore require further attention in future model development. Although spatially lumped models provide better predictions of sediment yield at the basin scale, and while validation of the predicted spatial patterns of sources and sinks of sediment requires further research, spatially distributed models are expected to be of value to support management decisions regarding the assessment of on-site and off-site impacts of erosion at the regional scale.     

Role of Fracturing in the Organization of the Karst Features of Azrou Plateau (Middle Atlas,Morroco) Studied by Remote Sensing Imagery

Karst formation geometry can be controlled by fractures and faults, and by other lithologies. Here we show the organization of kastic collapse features related to structures and to extensive basaltic lava flows in the Middle Atlas of Morocco. A lineament map of major faults and fractures has been created for the Middle Atlas using Landsat 7 ETM⁺ satellite images. This shows a dominant NE–SW regional direction and less prominent NNW–SSE and ENE–WSE directions. All these directions coincide with the alignments of karstic depressions that have formed in the Liassic limestones. The basaltic flows covering these formations on the Middle Atlas limestone plateau, have allowed the generation of cryptokarst, geometrically organized a long these major lineament directions. Karst landforms probabaly existed before the eruption of the lavas, but there were partly invaded by intrusions and volcanism. The extensive basaltic flows allowed for increased infiltration, and subsurface water flow, increasing the rate of kast formation after eruptions. Some basins show evidence of increased subsidence after lava emplacement (Aguelmam Sidi Ali Lake) and some maar-like craters also have subsided after eruption, by karts formation. We lay out the structural and lithological controls on Karstic formation in an intraplate volcanic field based on limestones and evaporites.     

Assessing sedimentation in a temperate dystrophic lake in the NE Atlantic seaboard region

Organic materials deposited in lacustrine environments can be derived from both aquatic and terrestrial ecosystems, and can serve as valuable indicators of catchment and in-lake ecological changes over time. However, spatial and temporal variation in the deposition of these materials within a lake basin will influence the interpretation of these sediment deposits. In this study, materials deposited in suspended sediment traps and basin sediments in Lough Feeagh, a temperate coastal humic lake, show variations in organic matter, total organic carbon and nitrogen loads, algal pigment concentrations and diatom assemblages. Sediment trap samples from three locations along with adjacent surface sediment cores show a clear north–south (inlet to outlet) gradient. C/N ratios reflected a mixture of algal and land-derived organic matter with a major peat influence, and comparisons between sediment trap and surface sediment assemblages revealed pigment and diatom assemblages influenced by lake-basin position and water depth. While some coherency between trap and sediment samples was apparent a more complicated biological response is demonstrated along with reduced water clarity in recent years thus highlighting the implications of increased allochthonous imputs for biological and biogeochemical processes in oligo-humic aquatic systems.     

First record of Branchinella spinosa (Milne-Edwards) (Crustacea: Branchiopodacolon; Anostraca) from Greece

As the result of a first screening of temporary inland water habitats,Branchinella spinosa is here recorded for the first time in Greece. This finding extends the circum-Mediterranean part of its vast distribution. The species was collected from a shallow astatic coastal salt-marsh that is mainly fed by rainwater, where it coexists but rarely co-occurs withArtemia parthenogenetica. Branchinella spinosa is only the fourth anostracan species currently known from Greece. The poor knowledge of anostracan richness and abundance is mainly due to limited sampling efforts in this area. As temporary aquatic habitats are threatened by several anthropogenic activities, especially agriculture and land clearing for urbanisation and tourism, there is an urgent necessity for further monitoring and protection of these precious habitats.     

Proton acceleration in flares and magnetohydrodynamic solar activity

The possibility of accelerated protons in solar flares having a sharp change in their spectral index is discussed. The analysis is based on the Tsytovich (1982, 1984, 1987a, b, c) acceleration model by MHD turbulence, which is shown to have different resonant conditions for non-relativistic and relativistic particles. The different resonant condition is shown to result in a sharp change in the accelerated proton spectral index, even in the absence of any peculiarity in the spectra of the MHD turbulence. Time scales for accelerated protons to relativistic energies are also derived, and shown to be consistent with observations. We also show that the threshold energy for electron acceleration by low frequency MHD turbulence is much greater than for proton acceleration. The turbulence therefore preferentially accelerates protons.     

Boundaries Make a Difference: The Effects of Spatial and Temporal Parameters on Conservation Planning*

Conservation planning and resulting ecological target identification require selection of both a planning area boundary and temporal baseline or reference condition. We examined the effects that these selections can have on resulting amount and location of identified conservation targets. A gap analysis for California was conducted using five different sets of ecoregion boundaries to identify and compare existing conservation shortfalls in major land cover type representation in protected areas using a threshold of 30 percent per ecoregion per type as the minimum required for future ecological viability. Another gap analysis was run for a single ecoregion using two temporal baselines (current and pre-1900) for the land cover followed by a comparison of identified conservation needs. We found that the boundaries of different ecoregional schemes affected both the total area needed to meet the per ecoregion land cover conservation goals and the spatial location of underprotected land cover types. Choice of temporal baseline also had a significant effect on the establishment of conservation targets for the highly human-impacted Central Valley ecoregion. To meet the given conservation threshold using a historic rather than contemporary baseline, a substantial amount of restoration is required. The results can help identify areas of both conservation needs consensus and those that vary widely based on the chosen planning boundary, as well as aid in the selection of appropriate restoration targets in degraded ecosystems. Because all landscapes are continuous in nature and planning area boundaries are discrete, similar results are likely to be found in analyses conducted in other regions.